This invention relates to a push button switch, and more particular to a push button switch of the interlocking/single-acting type with a simultaneous locking preventing function wherein, when one of a pair of juxtaposed sliders is in a non-locked condition, the other slider makes a single action wherein it is alternately locked and released by depressing operations thereof, but when one of the sliders is in a locked condition, the other slider itself is brought into a locked condition and releases the one slider from its locked condition thereby making an interlocking action, and when the two sliders are depressed at the same time, they are prevented from being locked simultaneously.
A switch of such an interlocking/single-acting type normally includes a push lock mechanism which is constituted from a cam groove having a heart-like configuration and an actuator pin for tracing the cam groove. For example, a push button switch disclosed in Japanese Patent Laid-Open No. 61-47027 includes a pair of actuator pins each supported for rocking motion on a slider, and a cam plate supported for rotation on an inner wall of a casing and having a pair of heart-shaped cam grooves formed thereon, whereby the cam plates are each rotated by the corresponding actuator pin. Accordingly, if one of the sliders is depressed, the driving pin thereon traces the corresponding cam groove, making a single action of the two sliders. On the other hand, if one of the sliders is depressed when the other slider is in a locked condition, the actuator pin on the depressed slider is locked while the cam plate is rotated by the actuator pin to release the other slider from its locked condition, making an interlocking action of the two sliders.
Meanwhile, in case a simultaneous locking preventing function is required for such an interlocking/single-acting switch, normally a simultaneous locking preventing plate is located between two sliders for movement in a direction perpendicular to the direction of reciprocal movement of the sliders so that it may prevent simultaneous locking of the sliders though this is not disclosed in Japanese Patent Laid-Open No. 61-47027 mentioned above. In the arrangement, upon single action by depression of only one of the two sliders, the simultaneous locking preventing plate is pushed by the one slider to move toward the other slider, but otherwise when the two sliders are depressed at the same time, opposite ends of the simultaneous locking preventing plate are abutted with the sliders at the same time thereby to prevent further movement of the sliders and thus prevent simultaneous switching of two circuits.
However, with the push button switch having such a construction as described above, since a locked condition of the actuator pin by the cam groove is released by rotation of the cam plate, there is the possibility that, upon such releasing, a locking step or shoulder of the cam groove may be abutted hard with an end of the actuator pin and the cam groove may be deformed by such hard abutment. Further, in order to assure a single action of the switch device, such a locking step must necessarily have a sufficient depth, and to this end, the rotational angle of the cam groove for releasing of a locked condition must be sufficiently great. Accordingly, a spacing for allowing rotation of the cam plate over a great angle is required, which obstructs miniaturization of the push button switch. However, if the cam plate does not have a sufficiently great rotational angle, a problem will give rise that a single action of the push button switch is not assured. Further, where the simultaneous locking preventing function is provided, the simultaneous locking preventing plate is required in addition to a push lock mechanism, and the push button switch is disadvantageous in miniaturization also in this regard.